Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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470 FXUS63 KDTX 250918 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 518 AM EDT Tue Jun 25 2024 .KEY MESSAGES... - A thunderstorm complex moves through central and southern Lower Michigan this morning. The system will be capable of strong to locally damaging wind gusts and possibly flooding rainfall. - An additional round of thunderstorms is possible tonight into early Wednesday, mainly along and south of the I-94 corridor to the Ohio border. - Cooler and less humid air moves back into the area by Wednesday night and lasts through Thursday. - The next chance of showers and thunderstorms arrives Friday night into Saturday. && .AVIATION... Strong, heavy rain producing thunderstorms impact southeast Michigan this morning, as the MCS tracks through 12-17z. The main impacts will be lowered visibility in heavy downpours and an isolated strong wind gust. Warmer air arrives on a breezy southwest wind (gusts to 25 knots) this afternoon with a slight chance for additional convection to develop as the cold front moves through late. Chances too low to include in tafs, with higher chance of a shower/thunderstorm on Wednesday as an upper level wave tracks through the state. For DTW/D21 Convection...TSRA window remains the same in this forecast (13z-16z). These storms will bring locally heavy downpours and possibly isolated wind gusts. Low chance of storms redeveloping this evening, but expectations is the activity will reside mainly south of the Michigan border. If thicker mid clouds are not around tonight, visibility could lower to MVFR or lower, as surface dew pts remain elevated in the mid 60s. DTW THRESHOLD PROBABILITIES... * High for ceilings aob 5kft Tuesday roughly 13-20z, then low. * High in thunderstorms late this morning (13-16z), then low. && .PREV DISCUSSION... Issued at 358 AM EDT Tue Jun 25 2024 DISCUSSION... Multiple convective clusters blossomed across the upper Midwest since sunset and are the forecast focus for Lower MI through this morning. The northern WI cluster became dominant in a location where mesoscale low pressure focused strong acceleration of the low level jet. Aggressive transport of moisture and instability now continues along and ahead of the southward extending surface warm front that marks the instability axis attracting persistence the existing storm complex or new storm development through the early morning cycle of nocturnal/elevated instability generation. This presents both a severe storm and excessive rainfall hazard across central and southern Lower MI this morning. There is room for additional upscale growth of the main northern WI convective cluster into full MCS organization which gives it a chance to overcome instability limitations with eastward extent into SE Lower Mi. Zonal 50 kt flow at 500 mb is a marker for enough shear to maintain balance long enough for sufficient strengthening of the low level cold pool and rear inflow. The mesoscale forcing then becomes strong enough for the system to remain surface based as the larger scale instability axis leans into western Lower MI toward sunrise where the strongest and most organized part of the system is favored to track. We also have to assume the eastern flank will be capable of severe intensity until it is proven the sharp eastward instability gradient can take a toll on the MCS strength as it tracks toward the Tri Cities and Thumb shortly after sunrise, and farther toward the I69 corridor by mid morning. A more typical weakening trend then continues late morning due to both weakening of the low level jet and veering/weakening inflow. This leaves more of a heavy rainfall threat in place for the Detroit metro area southward until the remains of the system exit into Ontario and Ohio by early afternoon. Conditions across SE MI will be stabilized considerably this afternoon, first by rain-cooled boundary layer air and then by warm temperatures aloft for the remainder of the day. A substantial west to east outflow boundary ends up south of the Ohio border which is later joined by the trailing surface trough that forces the instability axis into a similar west to east configuration by this evening. Additional surface based storms will be slow to develop along the hybrid outflow/prefrontal trough due to the capping aloft and little to no additional forcing on the heels of the early day system. Instead, another round of low level jet forced thunderstorm complexes are likely to initiate upstream where another round of surface low pressure is projected to form. This wave runs eastward along the surface trough keeping showers and storms mainly along and south of the IN/OH border until merging with the next northern stream mid level short wave. Showers and weaker storms spread back into SE MI Wednesday morning until the primary cold front sweeps through in the afternoon. Cooler and less humid air follows the Wednesday front which brings high temperatures back down into the 70s across the area by Thursday. Broad high pressure settles over the region Thursday into Friday but is kept moving by the large scale upper air pattern that maintains a progressive character through next weekend. MARINE... Remnant convection from WI/western Great Lakes works into the central Great Lakes this morning bringing the potential for a few strong/severe wind gusts within thunderstorm activity. These showers and storms clear the area by midday though a slow moving cold front dropping through the area will offer another window for showers and storms to redevelop latter part of today. These chances are mainly focused over the southern Great Lakes. Breezy SW conditions in advance of said front have led to the need for small craft advisories for all nearshore waters through much of the day today. An upper level trough settles into the Great Lakes Wednesday through late week bringing seasonably cooler conditions as well as more unsettled weather. HYDROLOGY... A complex of thunderstorms moves north to south across Lower Michigan this morning. Locally flooding rainfall is possible from this system as it produces widespread totals near 0.5 inch during the morning and isolated totals of 1 to 2 inches before exiting the area this afternoon. After a break during the afternoon, a second round of storms becomes possible tonight into Wednesday morning. The latest storm trends still support the best thunderstorm potential along and south of I94 where additional totals of 0.25 to 0.50 inch are likely and isolated totals up to 1 inch are possible until the pattern exits the area by Wednesday afternoon. The potential for flooding in each event is greater where repeated rounds of storms occur over the same area making ponding of water on roads and in prone low lying areas likely. The Tuesday and Wednesday activity collectively could lead to a brief response in the level of streams and rivers across the area through mid week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422- 441>443. Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon for LEZ444. && $$ AVIATION.....SF DISCUSSION...BT MARINE.......KDK HYDROLOGY....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.